The present invention relates to a tubular casing having a glued seam which exhibits advantageous adhesive and peelability properties. The present invention also relates to a process for the manufacture of the casing and its use as a sausage casing in the production of sausages.
Sausage casings having a glued seam are produced by folding a web into a tube along its longitudinal axis and gluing the overlapping edge zones running parallel to the longitudinal axis. Sausage casings of this type are described in European Offenlegungsschriften No. 0 037 543 and 0 054 162.
According to U.S. Pat. No. 2,607,696, an edge zone of a web of regenerated cellulose is provided with an acid aqueous solution of a partially polymerized, thermosetting urea/formaldehyde resin or melamine/formaldehyde resin, and the other edge zone of the web is then pressed together with the resin layer to form a tube. Subsequently, the overlapping edge zones are joined to one another at about 180.degree. to 220.degree. C. under the action of pressure, whereby the resin is thermoset. The resulting tubular casing can be used as a sausage casing for the production of small skinless sausages, in which the tubular casing can be peeled from the sausage after the boiling step.
This old process, which has been known for about 30 years, does not find any degree of applicability today, primarily because the overlapping seam is not of sufficient strength to withstand today's processing demands. For example, because of the relatively low breaking strength of the seam, there is an increased risk of bursting of the sausages made with this casing. In addition to the strength considerations, the known tubular casing can be manufactured only by a relatively complicated method. Furthermore, the high temperatures during gluing lead to an undesirable loss of water and to a permanent deterioriation of the physical properties of the web material, so that the tubular casing obtained is not suitable, for example, for the subsequent shirring necessary to produce shirred casings, hereinafter referred to as shirred sticks. On the other hand, heating to temperatures of above 180.degree. C. is necessary after the application of adhesive, in order to obtain any bond at all between the mutually overlapping edge zones of the web. Additionally, the ease of peeling of these sausage casings is unsatisfactory, and there is no suggestion to apply an internal coating in order to improve the ease of peeling.
Because of these disadvantages, tubular casings for foodstuffs, in particular artificial sausage casings have been manufactured predominantly from seamless material, although some disadvantages must be accepted in the case of these seamless tubular casings. In particular, this process is very cost-intensive. Another disadvantage is the presence of weakened zones, so-called extrusion edges, which run parallel to the longitudinal axis in the edge region on the edges which result from the tube being laid flat during the regeneration. Moreover, the stretching processes which are customary with seamless tubes also have disadvantages.
The internal coating which is required if a seamless tubing is to be used as an easily peelable sausage casing has to be applied to the inside of the seamless tube by a technically complicated process which is susceptible to disturbances. For example, the solution or dispersion must be introduced into the tubing by a time-consuming, separate process step, whereby it is necessary to cut the tubing open. Moreover, so far no suitable internal coating has been proposed which improves the peelability of casings with a glued seam, and in particular, no coating of this type has been proposed which does not negatively affect the adhesive present in the seam zone. U.S. Pat. No. 3,898,348 discloses the use of cellulose ethers, together with an oil, for internally coating tubings. In this process, a homogeneous, aqueous emulsion must be applied and the amount of the oil component must be small, as compared with the amount of cellulose ether. This coating cannot be used for glued tubings, however, because it significantly reduces the strength of the glued seam.